The present invention relates to a phase modulator apparatus, and more particularly to a phase modulator apparatus for generating a burst phase-modulated wave, which is used in a burst signal communication system such as a TDMA (Time Division Multiple Access) communication system and an MD-TDM (Multi Directional-Time Division Multiplex) communication system.
A conventional phase modulator apparatus of this kind includes a carrier generator for generating a carrier wave, a phase modulator for phase-modulating the carrier wave with an input information signal, an amplifier for amplifying the output of this phase modulator, a power source for supplying a source voltage to the oscillator, and the phase modulator and the amplifier. A switch turns on and off the source voltage supplied to the amplifier in a time-division burst mode. This switch provides a phase-modulated burst wave from the output of the amplifier.
In such an apparatus, when the source voltage is turned on or off in a time-division burst mode, the current supplied from the power source varies, thereby giving rise to fluctuations in voltage drop due to minute resistances which are present on the power supply line. As a result, the carrier frequency of the oscillator is varied to adversely affect the modulating performance.